Re: Conceptually not bad but ...
I can't eat or drive potential wealth
Nobody said you could. Wealth is potential, it allows you to do things. Even for your "growing food" example you have requirements: Seeds, agricultural surfaces, water, workforce, and finally transport and storage. If one of those is missing, you simply can't grow crops (for instance).
As for limiting wealth to Earth, you're right on a theoretical level, but we actually are restricted to Earth (so far), everything else is still Science Fiction. And of course, as Charles already said, asteroid resources are finite too.
You have to let go of the common, and very human way of thinking that amounts big enough equal infinity.
it turns lower value resources into higher human-valued items
There is that subjective value bias again. The objective (real) value of an iThing (to stay with that example) is simply the sum of its materials and the work put into making it (designing it, refining materials, assembling, transporting to the point of sale). I don't deny it has huge sentimental value for iThing fans, but so had some seashells to primitive civilization, would you count them as having added value to the global economy?
Biting the hand that feeds IT
